1. Field of the Invention
The invention relates to a production apparatus and a production method for an electric storage material.
2. Description of Related Art
Recently, a lithium ion secondary battery has been used in a hybrid vehicle, an electric vehicle or the like. Each of electrodes in the lithium ion secondary battery is produced by kneading a powder of an active substance and the like in a solution of a thickener to produce a slurry of an active material (electric storage material), applying the produced slurry to a base material such as an aluminum foil, and drying the slurry.
As described in Japanese Patent No. 4941692, the active substance is produced by applying microwaves to a precursor of the active substance, and maturing the precursor at a low temperature. Further, the slurry of the active material is produced by introducing the thickener, a solvent, the powder of the active substance, and the like together into a kneading device, agitating them so that the powder of the active substance and the like are dispersed while the thickener is dissolved in the solvent, and kneading the slurry of the active material until a predetermined viscosity is obtained.
At this stage, in order to increase the efficiency in dispersing the powder of the active substance and the like in the slurry, ultrasonic waves are applied to the slurry so as to vibrate the powder of the active substance and the like, as described in, for example, Japanese Patent No. 4104645, Japanese Patent Application Publication No. 2011-228062, Japanese Patent Application Publication No. 2006-310120 and Japanese Patent Application Publication No. 2005-276502. Further, in order to increase the efficiency in utilizing the powder of the active substance and the like in the slurry, microwaves are applied to the slurry so as to heat the powder of the active substance and the like, as described in, for example, Japanese Patent Application. Publication No. 2000-306598.
In general, it is difficult to dissolve the thickener in the solvent. For example, in the case where a powder of carboxymethylcellulose is used as the thickener, and water is used as the solvent, the powder of carboxymethylcellulose is gelled when it absorbs the water. Since the powder of carboxymethylcellulose is gelled, it becomes difficult for the water to deeply penetrate into the powder of carboxymethylcellulose. As a result, it is difficult to dissolve all the powder of carboxymethylcellulose in the water. Thus, in the conventional case where the thickener, the solvent, the powder of the active substance and the like are introduced together into the kneading device, and are agitated and kneaded, the kneading time tends to become long. If the kneading time becomes long, the active substance is subjected to shearing force for a long time, and therefore, the active substance may be damaged, and thus, it may be difficult to obtain high battery performance.
In general, as the viscosity of the slurry of the active material becomes lower, the initial battery performance becomes higher, but it becomes more difficult to appropriately perform an applying step and a drying step, which are steps performed after the kneading step. Thus, the viscosity of the slurry of the active material is adjusted to a predetermined value in view of the balance between the initial battery performance and the efficiency in performing the applying and drying steps. The adjustment of the viscosity of the slurry of the active material is performed by cutting molecular chains of the thickener with the use of shear energy that is obtained during the kneading of the powder of the active substance and the like in the solution of the thickener. Accordingly, production efficiency can be increased by kneading the powder of the active substance and the like at a high speed. However, if the kneading is performed at a high speed, the active material may be damaged, and it may be difficult to ensure high battery performance.